Nickel base alloy

ABSTRACT

A NICKEL BASE ALLOY CONSISTING ESSENTIALLY OF, IN WEIGHT PERCENT, UP TO 0.18% CARBON, FROM 14.2 TO 20% COBALT, FROM 13.7 TO 16% CHROMIUM, FROM 3.8 TO 5.5% MOLYBDENUM, FROM 2.75 TO 3.75% TITANIUM, FROM 3.75 TO 4.75% ALUMINUM, UP TO 4% IRON, FROM 0.005 TO 0.035% BORON, UP TO 0.5% ZIRCONIUM, UP TO 0.5% HAFNIUM, UP TO 0.75% COLUMBIUM, UP TO 0.5% RHENIUM, UP TO 0.75% TANTALUM, UP TO 1.0% MANGANESE, UP TO 3.0% TUNGSTEN, UP TO 0.5% RARE EARTH METALS, BALANCE ESSENTIALLY NICKEL WITH INCIDENTAL IMPURITIES, AND HAVING AN AVERAGE GRAIN SIZE COARSER TAN ASTM NO. 4 AND A MORPHOLOGY COMPRISED OF GAMMA PRIME PARTICLES WHICH CONSISTS ESSENTIALLY OF RANDOMLY DISPERSED IRREGULARLY SHAPED PARTILES LESS THAN ABOUT 0.35 MICRONS IN DIAMETER.

3 Sheets-Sheet 1 Filed Feb. 1, 1972 Q0 Qm fwmu NO/J 790/073 1 NJO/JdJuly 24, 1973 w. J. BOESCH NICKEL BASE ALLOY 3 Sheets-Sheet 2 Filed Feb.

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July 24, 1973 w. J BOESCH 3,748,192

NICKEL BASE ALLOY Filed Feb. 1, 1972 3 Sheets-Sheet 3 3,748,192 NICKELBASE ALLGY William J. Boesch, Utica, N.Y., assignor to Special MetalsCorporation, New Hartford, N.Y. Continuation-impart of application Ser.No. 42,412, June 1, 1970. This application Feb. 1, 1972, Ser. No.222,504 The portion of the term of the patent subsequent to Apr. 4,1989, has been disclaimed Int. Cl. (22c 19/00 US. Cl. 148-325 10 ClaimsABSTRACT F THE DISCLQSURE A nickel base alloy consisting essentially of,in weight percent, up to 0.18% carbon, from 14.2 to 20% cobalt, from13.7 to 16% chromium, from 3.8 to 5.5 molybdenum, from 2.75 to 3.75%titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to0.035 boron, up to 0.5% zirconium, up to 0.5% hafnium, up to 0.75columbium, up to 0.5% rhenium, up to 0.75 tantalum, up to 1.0%manganese, up to 3.0% tungsten, up to 0.5% rare earth metals, balanceessentially nickel with incidental impurities, and having an averagegrain size coarser than ASTM No. 4 and a morphology comprised of gammaprime particles which consist essentially of randomly dispersedirregularly shaped particles less than about 0.35 micron in diameter.

This application is a continuation-in-part of copending application Ser.No. 42,412 filed June 1, 1970, now Pat. No. 3,653,987.

The present invention relates to a nickel base alloy and moreparticularly to a nickel base alloy with improved high temperatureproperties.

Nickel base alloys have been known and used at elevated temperatures forquite some time. In particular, it is known that nickel base alloys canbe markedly improved by employing a precipitation hardening mechanism sothat their useful life is not only prolonged, but so the alloy can beused at higher temperatures. Perhaps the best known strengtheningprecipitate in nickel base alloys is the intermetallic compound known asgamma prime. Gamma prime is believed to have the general composition M(Al, Ti). As used herein, the M portion of the gamma prime compositionis regarded as consisting mainly of nickel with some substitution ofchromium and molybdenum and is considered to have the approximate atomicproportions, 95 nickel, 3 chromium, and 2 molybdenum.

I have found that the already good high temperature properties of nickelbase alloys consisting essentially of, in weight percent, up to 0.18%carbon, from 14.2 to 20% cobalt, from 13.7 to 16% chromium, from 3.8 to5.5% molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75%aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5%zirconium, up to 0.5% hafnium, up to 0.75% columbium, up to 0.5%rhenium, up to 0.75% tantalum, up to 1.0% manganese, up to 3.0%tungsten, up to 0.5% rare earth metals; e.g. cerium and/or yttriumand/or lanthanum, balance essentially nickel with incidental impurities,can be materially improved if the alloys are treated to develop aparticular gamma prime morphology and an average grain size coarser thanASTM No. 4. The particular morphology is comprised of gamma primeparticles which consist essentially of randomly dispersed irregularlyshaped particles less than about 0.35 micron in diameter.

In the past nickel base alloys having the composition described in thepreceding paragraph often had a morphology comprised of oriented cubicgamma prime particles about 0.5 micron per side. These cubic gamma primeparticles adversely atfected the alloys high tem- "United States PatentOffice Patented July 24, 1973 perature properties as they tended toagglomer-ate during prolonged elevated temperature service and formrod-like particles in certain crystallographic planes along which sliprapidly occurs. Formation of these cubic gamma prime particles was dueto the high temperatures employed during the second stage of the priorart heat treatments, during which gamma prime precipitation isinitiated. The heat treatment described herein avoids the formation ofcubic gamma prime by employing a maximum second stage temperature of1850 F. A particular prior art heat treatment used a second stagetemperature of 1975 F. It comprised the steps of: (l) heating at atemperature of 2135 F. for 4 hours and cooling; (2) heating at atemperature of 1975 F. for 4 hours and cooling; (3) heating at atemperature of 1550 F. for 24 hours and cooling; and (4) heating at atemperature of 1400 F. for 16 hours and cooling.

It is accordingly an object of this invention to provide a nickel basealloy with improved high temperature properties.

The foregoing and other objects of this invention will be bestunderstood from the following description, reference being had to theaccompanying drawing and photomicrographs wherein:

FIG. 1 is a plot of percent elongation versus time for two samples of anickel base alloy which underwent different second stage heat treatmentsat 1975 F. for 4 hours and at 1700 F. for 8 hours;

FIG. 2 is a photomicrograph at 7200 of a nickel base alloy whichunderwent a second stage heat treatment at 1975 F. for 4 hours,

FIG. 3 is a photomicrograph at 7200 of a nickel base alloy whichunderwent a second stage heat treatment at 1700 F. for 8 hours;

FIG. 4 is a photornicrograph at 7200 of a nickel base alloy whichunderwent a second stage heat treatment at 1750" F. for 8 hours; and

FIG. 5 is a photomicrograph at 7200 of a nickel base alloy whichunderwent a second stage heat treatment at 1750 F. for 24 hours.

The alloys of the present invention have a composition consistingessentially of, in weight percent, up to 0.18% carbon, from 14.2 to 20%cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from2.75 to 3.75% titanium, from 3.75 to 4.75 aluminum, up to 4% iron, from0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5% hafnium, up to0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum up to 1.0%manganese, up to 3% tungsten, up to 0.5% rare earth metals, e.g., ceriumand/or yttrium and/or lanthanum, balance essentially nickel withincidental impurities and a morphology comprised of gamma primeparticles which consist essentially of randomly dispersed irregularlyshaped particles less than about 0.35 micron, preferably 0.25 micron, indiameter. In addition the alloys can have other precipitates such as anM C precipitate (M is generally chromium) which improves grain boundaryductility. Alloys are respectively considered to be within the scope ofthe invention and within the preferred embodiment of the invention evenif they have occasional gamma prime particles (gamma prime particleswhich constitute less than five volume percent) in excess of 0.35 and0.25 micron. In most instances, the gamma prime particles of thepreferred embodiment range between 0.1 and 0.25 micron. The averagegrain size of the alloys is coarser than ASTM No. 4 and generallycoarser than ASTM No. 3. As a general rule, coarse grain alloys have agreater strength at elevated temperatures; e.g. 1800" F. than do finegrain alloys.

To illustrate the nickel base alloy of the present invention, referenceis directed to Table I which describes 1 Maximum.

A heat treatment for producing the particular grain size and morphologyfor the alloy of the present invention is described in the followingparagraphs. It is a two and preferably three stage treatment; i.e. twoor three heatings each followed by cooling.

The first stage of the heat treatment is designed to put sufficientcoarse gamma prime particles which form during alloy production, e.g.,during casting and working, into solution. Particles begin to go intosolution at a temperature of about 2000 F. (give or take about 25 F.,depending upon furnace accuracy) and solutioning is complete at about2125 F. The particular solutioning temperature employed depends upon theultimate use for the alloys. For alloys to be used at servicetemperatures in excess of 1800 F. it is preferable to use a solutioningtemperature in excess of 2125 F. as it is desirable to put substantiallyall the coarse gamma prime particles which do not contribute strength tothe alloy into solution. For alloys to be used at a service temperaturebelow 1800 F., e.g. 1400 F., it is sometimes desirable to use a partialsolutioning temperature of from 2000 F. to 2125 F. as the lowersolutioning temperature will produce an alloy with a finer grain size.In any event, the firststage must be controlled so as to produce analloy having an average grain size coarser than ASTM No. 4.

The second stage of the heat treatment is designed to initiate theformation of and form the randomly dispersed irregularly shaped finegamma prime particles and to form a. grain boundary precipitate, M (M isgenerally chromium) which improves grain boundary ductility. It is atime and temperature dependent process. At lower temperatures longertimes are involved and at higher temperatures shorter times. A lowertemperature limit of 1500 F. is imposed as it would be commerciallyimpractical to operate at lower temperatures when the time involved isconsidered. An upper temperature limit of 1850" F. is imposed as M 0begins to go into solution at this temperature and since the formationof cubic gamma prime particles is accelerated at higher temperatures. Apreferred temperature range is from about 1600 F. to about 1800 F. Norange can be placed upon the time period as it depends upon too manyvariables such as the temperature and thickness of the material beingtreated.

The third stage of the heat treatment is preferable and not necessary.It is designed to precipitate additional M C particles and is performedat a temperature low enough to preclude detrimental gamma prime particlegrowth. The temperature range for this stage of the heat treatment is1350-1450 F.

The following examples are illustrative of the invention.

Several samples (Samples A, B, C and D) were melted, heat treated, andphotomicrographed. In addition, Samples A and B were tested for creep at1800 F. under a stress of 16 k.s.i. The samples had a compositionconsisting essentially of, in weight percent, 0.88% carbon, 16.9%cobalt, 15.1% chromium, 5.0% molybdenum, 3.47% titanium, 4.0% aluminum,0.027% boron, balance essentially nickel with incidental impurities.Sample A was given a heat treatment which comprised the steps of: (1)heating at a temperature of 2135 F. for 4 hours and air cooling; (2)heating at a temperature of 1975 F. for 4 hours and air cooling; (3)heating at a temperature of 1550 F. for 24 hours and air cooling; and(4) heating at a temperature of 1400 F. for 16 hours and air cooling.Sample B was given a heat treatment which comprised the steps of: (1)heating at a temperature of 2135 F. for 4 hours and air cooling; (2)heating at a temperature of 1700 F. for 8 hours and air cooling; and (3)heating at a temperature of 1400 F. for 16 hours and air cooling. SampleC was heat treated in the same manner as Sample B with the exceptionthat the intermediate heating, i.e., the second stage heating, was at atemperature of 1750 F. Sample D was heat treated in the same manner asSample B with the exception that the intermediate heating was at atemperature of 1750 F. for a 24-hour period.

The results of the creep tests for Samples A and B are shown in FIG. 1wherein percent elongation is plotted versus time. A study of theresults reveals that Sample B, which was given a heat treatment withinthe scope of this invention, had a lower second stage creep rate, i.e.,the substantially constant creep rate commonly used for design purposes,than did Sample A which was given a conventional prior art heattreatment. Samples B and A had respective second stage creep rates of0.006% hour and 0.04% /hour. A part with a specification of 1% maximumcreep at 1800" F. under a stress of 16 k.s.i. would have a useful lifeof about 10 hours with the conventional heat treatment given Sample Aand a useful life of about hours with the improved heat treatment givenSample B. Sample B, therefore, shows an 11 to 1 improvement over SampleA.

Photomicrographs at 7200 show the different morphologies of Samples Aand B. FIG. 2, which is the photomicrograph of Sample A, is comprised oforiented cibuc gamma prime particles about 0.5 micron per side (some ofthe gamma prime particles have a triangular or trapezoidal appearancedue to the grain orientation and surface intersection) and FIG. 3, whichis the photomicrograph of Sample B, is comprised of gamma primeparticles which consist essentially of randomly dispersed irregularlyshaped gamma prime particles which are less than about 0.25 micron indiameter. The photomicrographs clearly show that the lower second stagecreep rate of Sample B is due to its particular morphology which resultsfrom the particular heat treatment of this invention.

The photomicrographs of FIGS. 4 and 5 show how the time and temperatureof the second stage of the heat treatment of this invention affects thesize of the gamma prime particles. Sample C, which was treated in thesame manner as Sample B with the exception that the intermediate heatingwas at a temperature of 1750 F. instead of 1700 F., had gamma primeparticles larger in size than the gamma prime particles of Sample B andSample D which was treated in the same manner as Sample C with theexception that the intermediate heating was for 24 hours instead of 8hours, had gamma prime particles larger in size than the gamma primeparticles of Sample C. Samples C and D are respectively shown at 7200 inFIGS. 4 and 5.

Several additional samples (Samples E, F, G and H) were melted, heattreated, and stress rupture tested at 1650 F. under a stress of 35k.s.i. The samples had a composition consisting essentially of, inweight percent, 0.05% carbon, 17.5% cobalt, 14.5% chromium, 4.5%molybdenum, 3.19% titanium, 4.20% aluminum, 0.028% boron, balanceessentially nickel with incidental impurities. Sample E was given a heattreatment which comprised the steps of: (1) heating at a temperature of2135 F. for 4 hours and air cooling; (2) heating at a temperature of1975 F. for 4 hours and air cooling; (3) heating at a temperature of1550 F. for 24 hours and air cooling; and (4) heating at a temperatureof 1400 F. for 16 hours and air cooling. Sample F was given a heattreatment which comprised the steps of: (1) heating at a temperature of2135 F. for 4 hours and air cooling; (2) heating at a temperature of1700 F. for 4 hours and air cooling; and (3) heating at a temperature of1400 F. for 16 hours and air cooling. Samples G and H were heat treatedin the same manner as Sample F with the exception that the intermediateheatings were for respective periods of 8 and 16 hours.

The results of the stress rupture tests for Samples E, F,

1 Average of two specimens.

The data in Table II reveals that Samples F, G and H, which were givenheat treatments within the scope of this invention, had a longer lifethan did Sample E which was given a conventional prior art heattreatment. Sample G had an average life of 141.7 hours at 1650 F. undera stress of 35 k.s.i. with the heat treatment of this invention incomparison to an average life of 110.5 hours for Sample E which had aprior art heat treatment.

It will be apparent to those skilled in the art that the novelprinciples of the invention disclosed herein in connection with specificexamples thereof will suggest various other modifications andapplications of the same. It is accordingly desired that in construingthe breadth of the appended claims they shall not be limited to thespecific examples of the invention described herein.

1 claim:

1. A nickel base alloy having improved high temperature properties; saidalloy consisting essentially of, in weight percent, up to 0.18% carbon,from 14.2 to 20% cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5%molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75% aluminum, upto 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5hafnium, up to 0.75% columbium, up to 0.5% rhenium, up to 0.75%tantalum, up to 1.0% manganese, up to 3% tungsten, up to 0.5% rare earthmetals, balance essentially nickel with incidental impurities; saidalloy having an average grain size coarser than ASTM No. 4 and amorphology comprised of gamma prime particles which consist essentiallyof randomly dispersed irregularly shaped particles less than about 0.35micron in diameter.

2. A nickel base alloy according to claim 1 wherein said randomlydispersed iregularly shaped gamma prime particles are less than about0.25 micron in diameter.

3. A nickel base alloy according to claim 1 wherein said randomlydispersed irregularly shaped gamma prime particles are from about 0.1 to0.25 micron in diameter.

4. A nickel base alloy according to claim 1 which consists essentiallyof, in Weight percent, from 0.03 to 0.10% carbon, from 17 to 20% cobalt,from 14 to 16% chromiurn; from 4.5 to 5.5% molybdenum, from 2.75 to3.75% titanium, from 3.75 to 4.75 aluminum, up to 4% iron, from 0.025 to0.035% boron, up to 0.06% zirconium, up to 0.15% manganese, balancenickel with incidental impurities.

5. A nickel base alloy according to claim 4 wherein said randomlydispersed irregularly shaped gamma prime particles are less than about0.25 micron in diameter.

6. A nickel base alloy according to claim 1 which consists essentiallyof, in weight percent, from 0.03 to 0.09% carbon, from 16 to 18% cobalt,from 14 to 16% chromium, from 4.5 to 5.5 molybdenum, from 3.35 to 3.65%titanium, from 3.85 to 4.15% aluminum, up to 0.5 maximum iron, from 0.02to 0.03% boron, up to 0.10% zirconium, up to 0.15 manganese, balancenickel with incidental impurities.

7. A nickel base alloy according to claim 6 wherein said randomlydispersed irregularly shaped gamma prime particles are less than about0.25 micron in diameter.

8. A nickel base alloy according to claim 1 which consists essentiallyof, in weight percent, from 0.05 to 0.09% carbon, from 14.25 to 16.25%cobalt, from 14 to 15.25% chromium, from 3.9 to 4.9% molybdenum, from3.0 to 3.7% titanium, from 4 to 4.6% aluminum, up to 0.5% iron, from0.012 to 0.02% boron, up to 0.06% zirconium up to 0.15% manganese,balance nickel with incidental impurities.

9. A nickel base alloy according to claim 8 wherein said randomlydispersed irregularly shaped gamma prime particles are less than about0.25 micron in diameter.

10. A nickel base alloy according to claim 2 wherein said average grainsize is coarser than ASTM No. 3.

References Cited UNITED STATES PATENTS 3,536,542 10/ 1970 Murphy et al148-162 RICHARD O. DEAN, Primary Examiner U.S. Cl. X.R. -171; 148-162

